The advent of world-wide electronic communications systems has enhanced the way in which people can send and receive information. For example, the capabilities of real-time video and audio systems have greatly improved in recent years. In order to provide services such as video-on-demand, video conferencing, and motion picture playback, to name but a few, an enormous amount of bandwidth is required. In fact, bandwidth is often the main inhibitor in the effectiveness of such systems.
In order to overcome the constraints imposed by existing technology, compression systems have emerged. These-systems reduce the amount of video and audio data which must be transmitted by removing redundancy in the picture sequence. At the receiving end, the picture sequence is uncompressed and may be displayed in real time.
One example of a video compression standard is the Moving Picture Expert's Group (MPEG) standard. Within the MPEG standard (known as ISO/IEC 13818), video compression is defined within a picture and between pictures. Video compression within a picture is accomplished by conversion of the digital image from the time domain to the frequency domain by a discrete cosine transform, quantitization, variable length coding, and Huffman coding. Compression between pictures is accomplished by a process referred as “motion estimation”, in which a motion vector plus difference data is used to describe the translation of a set of picture elements from one picture to another. The ISO MPEG2 standard specifies only the syntax of a bit stream and semantics of the decode process. The particular choice of coding parameters and trade-offs in performance versus complexity are left to the system developers.
There is substantial interest in the computer and entertainment industries in incorporating video data in multimedia and related applications for use on processor-based video systems. Potential growth in this area has been enabled by development of video compression schemes, such as the above-summarized MPEG standard that reduce the amount of digital data required to display high quality video images, and by the development of storage media, such as digital video discs (DVDs) which can accommodate data in compressed form for an entire movie on a single compact disc. With the compressed data of an entire movie readily available on a single compact disc, content providers are naturally concerned with the possibility of unauthorized copying, and thus, desire to encrypt the compressed data wherever it may be available.
As digital transmissions (and storage) become more prevalent, the security of these transmissions becomes more important. The owners and distributors of any digital signal, such as a video conferencing signal or a direct-satellite transmission, may wish the signal to be unintelligible to unauthorized parties. A digital transmission of video (such as MPEG compressed data) can be protected by encrypting the data. Various encryption techniques exist in the literature for protecting a data stream. Decryption of the stream is then performed on the receiving end. Encryption and decryption might depend on a numerical key. Such a scheme, depending on the thoroughness of the encryption, may be secure for a time, but the stream is still susceptible to being intercepted and reverse engineered.
Thus, a more secure approach to encrypting a digital transmission, either within a system or between systems is deemed desirable.